This invention relates to drugs for use in cancer therapy. More specifically, the present invention concerns drugs which induce proliferation of cells of the hematopoietic system.
1. Prior Art
The following is a list of prior art references considered to be relevant as background to the invention:
1. Daly, J. W., Adenosine receptors: Targets for future drugs. J. Med. Chem., 25:197-207, 1982.
2. Stiles, G. L., Adenosine receptors and beyond: Molecular mechanisms of physiological regulation, Clin. Res., 38:10-18, 1990.
3. Collis, M. G., The vasodilator role of adenosine, Pharmacol. Ther, 41:143-162, 1989.
4. Fishman et al., Extracellular adenosine acts as a chemoprotective agent, Proceeding of the American Association for Cancer Research, 39:470, 1998.
5. Moos, W. H., et al., N6-cycloalkyladenosines. Potent A1 selective adenosine agonists, J. Medicinal Chemistry 28:1383-1384, 1985.
6. Jacobson, K. A et al., Functionalized congeners of adenosine, J. Medicinal Chemistry 28:1341-1346, 1985.
7. U.S. Pat. No. 5,998,387.
8. U.S. Pat. No. 5,998,388
9. U.S. Pat. No. 5,498,605.
10. U.S. Pat. No. 4,791,103.
2. Background of the Invention
Adenosine is an extracellular messenger generated by all cells in the body. It is known to regulate different physiological processes within cells through binding to specific cell surface receptorsxe2x80x94A1 and A2 receptors (1,2,3). It was recently demonstrated that adenosine inhibits proliferation of tumor cells and induces proliferation of bone marrow cells (4). Further more it was also shown that adenosine can protect white blood cells, particularly neutrophils, from destruction which is otherwise caused by chemotherapeutic drugs (4).
The present invention is based on the surprising findings that (i) the effect of adenosine in inducing proliferation of bone marrow cells can be inhibited by A1 receptor antagonists (antagonist that inhibits binding of adenosine to adenosine A1 receptor), and (ii) the effect of adenosine can be mimicked by an adenosine A1 receptor agonist (xe2x80x9cA1RAgxe2x80x9d). These findings led to the conclusion that the bone marrow proliferation-induction effect of adenosine is mediated, at least to some extent through the A1 receptor, and that accordingly A1RAg may be used to induce proliferation of bone marrow cells, in a wide variety of clinical situations where such proliferation is therapeutically beneficial.
The present invention provides, by a first of its aspects, a pharmaceutical composition for use in inducing proliferation of bone marrow cells, comprising a pharmaceutically acceptable carrier, excipient or diluent and, as an active ingredient, an effective amount of an A1RAg.
The present invention provides, by a second of its aspects, use of an A1RAg for the production of a pharmaceutical composition for use in inducing proliferation of bone marrow cells.
The present invention further provides a method of inducing proliferation of bone marrow cells in a subject, comprising administering to the subject an effective amount of an A1RAg.
The term xe2x80x9ceffective amountxe2x80x9d used above and below should be understood as meaning an amount of an A1RAg which is capable of achieving a desired therapeutic effect, particularly, in inducing proliferation of bone marrow cells. The desired therapeutic effect depends on the type and mode of treatment. When, for example, said A1RAg is administered to counter drug-induced leukopenia, an effective amount thereof may be an amount which protects the treated subject against the drug-induced reduction in the count of leukocytes, particularly neutrophils; an amount of the active ingredient which can give rise to an increase in an already decreased level of such cells, e.g. restore the level to a normal level or sometimes even above; etc. The man of the art will have no difficulties, on the basis of a limited number of routine experiments, to determine an effective amount in each case.
As will be appreciated, the effective amount may also depend on the treated subject""s gender, on the individual""s weight, on the therapeutic regime, namely whether the A1RAg is administered once daily, several times daily, once in several days, etc. Furthermore, the effective amount may depend on the exact nature or etiology of the disease or condition which is being treated or intended to be prevented.
According to one embodiment of the invention, the A1RAg are adenosine derivatives carrying at least an N6-substituent. Other positions may also be substituted. In fact, it has been found that the biological activity of an adenosine derivative may be enhanced by modifying other parts of the nucleotide, for example, at the 2- and/or 5xe2x80x2-positions (e.g. with chloro atoms). Such substituents were found to increase the molecule""s A1 selectivity.
The adenosine derivatives which can be used according to the present invention are generally defined by the following formula (I): 
wherein
R1 represents a lower alkyl, cycloalkyl, preferably C3-C8 cycloalkyl (including the well known cyclohexyl and cyclopentyl containing derivatives, recognized as CPA and CHA, respectively), the cycloalkyl group may be substituted with, for example, a hydroxyl or lower alkyl; R1 also represents a hydroxyl or hydroxyalkyl; a phenyl anilide, or lower alkyl phenyl, all optionally substituted by one or more substituents, for example, halogen, lower alkyl, haloalkyl such as trifluoromethyl, nitro, cyano, xe2x80x94(CH2)mCO2Ra, xe2x80x94(CH2)mCONR2R4Rb, xe2x80x94(CH2)mCORa, m representing an integer from 0 to 6; xe2x80x94SORc, xe2x80x94SO2Rc, xe2x80x94SO3H, xe2x80x94SO2NRaRb, xe2x80x94ORa, xe2x80x94SRa, xe2x80x94NHSO2Rc, xe2x80x94NHCORa, xe2x80x94NRaRb or xe2x80x94NHRaCO2Rb; wherein
Ra and Rb represent independently a hydrogen, lower alkyl, alkanoyl, phenyl or naphthyl (the latter may be partially saturated) the alkyl group optionally being substituted with a substituted or unsubstituted phenyl or phenoxy group; or when R1 represents xe2x80x94NRaRb, said Ra and Rb form together with the nitrogen atom a 5- or 6- membered heterocyclic ring optionally containing a second heteroatom selected from oxygen or nitrogen, which second nitrogen heteroatom may optionally be further substituted by hydrogen or lower alkyl; or xe2x80x94NRaRb is a group of general formulae (II) or (III): 
xe2x80x83wherein
n is an integer from 1 to 4;
Z is hydrogen, lower alkyl or hydroxyl;
Y is hydrogen, lower alkyl, or ORxe2x80x2 where Rxe2x80x2 is hydrogen, lower alkyl or lower alkanoyl;
A is a bond or a lower alkylene, preferably, C1-C4 alkenyl; and
X and Xxe2x80x2 are each independently hydrogen, lower alkyl, lower alkoxy, hydroxy, lower alkanoyl, nitro, haloalkyl such as trifluoromethyl, halogen, amino, mono- or di-lower alkyl amino, or when X and Xxe2x80x2 are taken together a methylenedioxy group;
Rc represents a lower alkyl;
R2 represents a hydrogen; halogen; substituted or unsubstituted lower alkyl or alkenyl group; lower haloalkyl or haloalkenyl; cyano; acetoamido; lower alkoxy; lower alkylamino; NRdRe where Rd and Re are independently hydrogen, lower alkyl, phenyl or phenyl substituted by lower alkyl, lower alkoxy halogen or haloalkyl such as trifluoromethyl or alkoxy; or xe2x80x94SRf where Rf is hydrogen, lower alkyl, lower alkanoyl, benzoyl or phenyl;
W represents the group xe2x80x94OCH2xe2x80x94, xe2x80x94NHCH2xe2x80x94, xe2x80x94SCH2xe2x80x94 or xe2x80x94NH(Cxe2x95x90O)xe2x80x94;
R3, R4 and R5 represent independently a hydrogen, lower alkyl or lower alkenyl, branched or unbranched C1-C12 alkanoyl, benzoyl or benzoyl substituted by lower alkyl, lower alkoxy, halogen, or R4 and R5 form together a five membered ring optionally substituted by a lower alkyl or alkenyl; R3 further represents independently a phosphate, hydrogen or dihydrogen phosphate, or an alkali metal or ammonium or dialkali or diammonium said thereof;
R6 represents a hydrogen, halogen atom; or
one of the R groups (i.e. R1 to R6) is a sulfohydrocarbon radical of the formula Rgxe2x80x94SO3xe2x80x94Rhxe2x80x94, wherein Rg represents a group selected from C1-C10 aliphatic, phenyl and lower alkyl substituted aromatic group which may be substituted or unsubstituted and Rh represents a monovalent cation. Suitable monovalent cations include lithium, sodium, potassium, ammonium or trialkyl ammonium, which will enable dissociation to take place under physiological conditions. The remaining R groups being a hydrogen or halogen atom, an unsubstituted hydrocarbon or any other non-sulfur containing group as defined above.
The active ingredient may be as defined above or in the form of salts or solvates thereof, in particular physiologically acceptable salts and solvates thereof. Further, when containing one or more asymmetric carbon atoms, the active ingredient may include isomers and diastereoisomers of the compounds of formula (I) and mixtures thereof.
The hydrocarbon chains used herein may include straight or branched chains. In particular, the terms xe2x80x9calkylxe2x80x9d or xe2x80x9calkenylxe2x80x9d as used herein mean a straight or branched chain alkyl or alkenyl groups.
The terms xe2x80x9clower alkyl or lower alkenylxe2x80x9d mean respectively C1-C10 alkyl or C2-C10 alkenyl groups and preferably, C1-C6 alkyl and C2-C6 alkenyl groups.
Pharmaceutically acceptable salts of the compound of general formula (I) include those derived from pharmaceutically acceptable inorganic and organic acids. Examples of suitable acids include hydrochloric, hydrobromic, sulphoric, nitric, perchloric, fumaric, maleic, phosphoric, glycollic, lactic, salicylic, succinic, toluene-p-sulfonic, tartaric, acetic, citric, methanesulfonic, formic, benzoic, malonic, naphthalene-2-sulfonic and benzenesulfonic acids.
Preferred adenosine derivatives of formula (I) are the N6-cyclopentyl adenosine (CPA), 2-chloro-CPA (CCPA), and N6-cyclohexyl adenosine (CHA) derivatives, the preparation of which is well known to the person skilled in the art. Other adenosine derivatives which are known to be selective to the A1 receptor are those wherein R1 is a anilide group, the latter may be unsubstituted or substituted for example with hydroxyl, alkyl, alkoxy or with a group xe2x80x94CH2C(O)Rxe2x80x3, Rxe2x80x3 being an hydroxyl group, xe2x80x94NHCH3, xe2x80x94NHCH2CO2C2H5, (ethyl glycinate), tuloidide (also in which the methyl moiety is replaced with a haloalkyl moiety), or with a group xe2x80x94CH2C(O)NHC6H4CH2C(O)Rxe2x80x2xe2x80x3, in which Rxe2x80x2xe2x80x3 represents a group to yield a methyl ester substituent (xe2x80x94OCH3), an amide substituent (e.g. Rxe2x80x2xe2x80x3 being a group xe2x80x94NHCH3), or Rxe2x80x2xe2x80x3 being a hydrazide, ethylenediamine, xe2x80x94NHC2H5NHC(O)CH3, 4-(hydroxyphenyl) propionyl, biotinylated ethylene diamine or any other suitable hydrocarbon which renders the compound an A1 agonist. The preparation of some of the above specific adenosine derivatives is described in the art (5-8) 
Alternatively, the N6-substituted adenosine derivatives used as active ingredients according to the present invention may be those containing an epoxide moiety and more particularly are a cycloalkyl epoxy containing adenosine derivative (e.g. oxabicyclo such as norbornanyl or oxatricyclo such as adamantanyl). Some such compounds may be defined by general formula (I),
wherein R1 is a group of general formulae (IVa) and (IVb): 
wherein M is a Lower alkyl group as defined above.
Embodiments of the agonist compounds having an epoxide N6-norbornyl group include the endo and exo isomers and more particularly, can be one of four isomers: the 2R-exo, 2R-endo, 2S-exo and 2S-endo form.
Another embodiment of the N6-norbornyl derivative may include an oxygen atom at the N1-position of the purine ring. This compound is termed N6-(5,6-epoxynorborn-2-yl)adenosine-1-oxide.
At times, the active ingredient nay be an adenine derivative in which the xcex2-D-ribofuranozyl moiety of adenosine is replaced with a hydrogen or phenyl group.
The invention has a wide range of therapeutic utilities and provides treatment for a wide range of diseases, disorders or conditions in both human and non-human animals, where induction of proliferation of bone marrow cells may be beneficial to the treated subject. Therapeutic applications include immunomodulation in a subject having a weak immune system, for example: as a result of a genetic disorder; as a result of an infection by an infectious agent, e.g. a virus; as a result of a general stress situation, e.g. following a car or another accident, etc.; as a result of a treatment which causes reduction in the level of leukocytes, particularly neutrophils, e.g. a chemotherapy or treatment with a neuroleptic drug; etc.
A treatment according to the invention may be used to reduce the risk of infection resulting from congenital or acquired neutropenias.
The present invention may also be used for the treatment of subjects having a low count of white blood cells, either a general low count or a count of a specific class of white blood cells, e.g. neutrophils. A weakened immune system manifested by a reduction in white blood cell count is often seen in cancer patients, and when this occurs, this may have a severe effect on the treated patent, and may at times even be a cause of death. In such a case it is thus important to try and increase the white blood cell count. This may be achieved by the treatment in accordance with the invention.
Reduction of white blood cell count, particularly of neutrophils, is very often an undesired side effect of a variety of treatments, including: anti-cancer therapy by chemotherapy or radiotherapy; treatment of a subject with neuroleptic drugs; etc. The active ingredient of the invention may be used in such subject to counter these undesired side effects of the treatment. In accordance with some therapeutic regimes, the active ingredient of the invention may be administered prior to such treatment, or concurrently therewith. For example, in the case of a treatment with a chemotherapeutic drug or treatment with a neuroleptic drug, the active ingredient of the invention may be administered either prior to the onset of treatment with the chemotherapeutic or the neuroleptic drug during such treatment, or may also at times be given after such treatment. In other words, the active ingredient of the invention may be used either as a preventive agent namely to prevent reduction of the white blood cell level as a result of the treatments or may be used as an acute therapeutic agent for simulating an increase in the level of the white blood cells after the level was reduced as a result of said treatment.
In accordance with one embodiment of the invention, an anti-cancer chemotherapeutic agent or a neuroleptic drug may be combined in one formulation with the active ingredient of the invention.